Document folders are widely used in office and study and frequently used in work. For example, the Chinese utility model Apl. No. 200720052528.9 titled “Document Folder” is provided. When a fastener for the document folder is opened, manpower is required for fastener opening and the state of fastener opening must be maintained. When the fastener for the document folder is closed, manpower is usually required for auxiliary and slow closing of the fastener so as to avoid the risk of pinching hand. In order to increase the clamping force of the fastener to the document folder, the torsional force of torsion springs fixed on rotating shafts of the fastener is larger. Therefore, when the state of fastener opening is maintained, a user can only use one hand to hold the fastener and the other hand to put documents in order, and thus the documents are usually out of order. When the fastener is closed, if the hand for holding the fastener is abruptly let go, a hook bracket of the fastener may revolve abruptly, and thus the other hand may be wounded due to the impact and holding of the hook bracket. The fastener for the document folder has the disadvantages that: when the fastener is opened, manpower is required for holding the fastener, and thus the sorting of the documents is inconvenient; and when the fastener is closed, the hands may be wounded.